Diagnosis of Thyroid Cancer

Diagnostic Evaluation of Thyroid Cancer

The initial steps in the diagnosis of thyroid cancer involve a complete medical history followed by a physical examination. In taking the medical history, your doctor will ask you to describe any signs and symptoms that you may have been experiencing and will also ask you specific questions to determine if you have any risk factors for thyroid cancer. The physician will then perform a physical examination and will check to see if you have an enlarged thyroid gland or enlarged cervical lymph nodes. If the results of the medical history and physical examination suggest the possibility of thyroid cancer, your doctor will order additional diagnostic tests to either confirm or rule out thyroid cancer. These tests may include:

• Fine needle aspiration cytology
• Radioactive thyroid scan
• Imaging studies

Fine Needle Aspiration Cytology

Fine needle aspiration cytology (FNAC) is a diagnostic technique that involves using a narrow gauge (25-22G) needle to obtain a sample of a suspicious tumor for microscopic examination to determine if it is malignant or benign. This diagnostic test is the "gold standard" for evaluating patients with thyroid nodules. In most cases, FNAC can help determine if the thyroid nodule is cancerous or non-cancerous. Fine needle aspiration cytology can also help doctors determine if a malignant thyroid tumor is papillary, follicular, medullary or anaplastic thyroid carcinoma.

Radioactive Thyroid Scan

This test measures the uptake of a radioactive substance (iodine or technetium) by the thyroid gland. This test cannot, however, determine if whether a thyroid nodule is malignant or benign. Once a thyroid nodule has been determined to be malignant by FNAC, a radioactive thyroid scan is useful for evaluating how far the cancer has spread (cancer staging). When radioactive iodine is used for diagnostic scans, the isotope is Iodine-123 and the radiation dose is much lower than when used for therapeutic scans.

Ultrasound Imaging

An ultrasound examination of the neck may be performed in patients with thyroid nodules to evaluate the number and size of the nodules as well as to visualize the cervical lymph nodes. If the nodule is found to be benign by FNAC, no treatment is required. Patients with benign thyroid nodules usually undergo a thyroid ultrasound scan every 6 to 9 months to determine if the nodule is increasing in size. A 15% or more increase in the size of a nodule on serial ultrasound imaging usually requires a repeat FNAC to determine if the nodule is malignant. Although ultrasound imaging cannot distinguish between benign and malignant thyroid nodules, the presence of small areas of calcification (microcalcification) by ultrasound is associated with papillary thyroid carcinoma in about 40% of cases.

Other imaging modalities such as computed tomography (CT scan) and magnetic resonance imaging (MRI) are not routinely used for the diagnosis of thyroid cancer but rather for determining how far the cancer has spread (cancer staging).